Production of ethylene oxide by contact gas-phase oxidation of ethylene with a catalyst and molecular-oxygen-containing gas has been industrially utilized widely. Although the technology has already been developed to a high level, in order to achieve further cost reduction, development of catalysts for producing ethylene oxide which exhibits superior performance in selectivity, durability, and the like has still been a research subject for researchers in this technical field.
It is well known that the performance of a catalyst for producing ethylene oxide is influenced by the size of metal silver particles supported on a carrier such as alumina, and hence trials to support metal silver as fine particles on a carrier have been done. Fact is, however, a catalyst for producing ethylene oxide comprising metal silver as fine particles supported on a carrier, which is superior in selectivity and durability and can be used industrially and advantageously, has not yet been realized.
Recently, a method for producing nano-sized fine metal particles by utilizing microwave has been proposed. For example, U.S. Pat. No. 6,387,494 B1 describes a method for producing nano-sized fine particles consisting of a metal derived from a metal salt by dissolving or dispersing the metal salt in a solvent, and then irradiating microwave thereto.
In addition, JP-A-2003-13105 describes a method for producing a carrier adhered with fine metal particles in which fine metal particles were adhered on the carrier, by mixing a solid material as carrier and a metal compound with ethylene glycol for example, and then irradiating microwave thereto.